1. Field of the Invention
The present invention relates generally to roof bolters and, more particularly, to a two-position roof bolter and process for resin bolting a mine roof.
2. The Prior Art
Underground mining, whether for coal or ore, is an old art. There are two principal methods of underground mining: room-and-pillar and longwall working. Room-and-pillar mining denotes a system of mining in which the coal or ore is mined in rooms (i.e., tunnels) separated by pillars. Room-and-pillar mining is preferred when mining beneath surface building or under lakes and seas. The pillars are preferably left in position to minimize movement of the ground at the surface. When the pillars are left in place, the term "partial extraction" is applied to this system of mining. In room-and-pillar mining, once access to the seam has been gained, rooms (i.e., tunnels) are driven into the seam in two directions and at right angles to each other. As a result, the seam is divided into a number of rectangular blocks of coal or ore, which rectangular blocks are called pillars. In contrast, longwall working is a "total extraction" system of mining. In longwall working, all the coal or ore contained within a specified area is extracted in one operation. To do this, two parallel tunnels (also known as gate roads) are driven into the seam some 150 to 600 feet apart. The two parallel tunnels are then connected by a third tunnel formed at right angles to the two parallel tunnels. This third tunnel forms the longwall face. Successive strips are than taken off the side of the longwall face and the coal (or ore) is deposited on a face conveyor. The face conveyor in turn delivers the coal to the gate road conveyor and hence to the shaft. As the longwall face moves forward, the roof behind the face is allowed to collapse. The gate roads (the tunnels) however are being correspondingly advanced and of course supported. It is to the support of these tunnels, be they gate roads or rooms, that the invention pertains. For the drilling of the tunnels themselves, see U.S. Pat. No. 3,552,504 to L. L. Chappuis.
One of the more effective ways to support the tunnels is by inserting roof bolts in predrilled holes in the roofs of the tunnels. (A roof bolt is a long steel bolt anchored into walls or roofs of underground excavations to strengthen the pinning of rock strata.) The roof bolts are installed into the roofs at substantially evenly spaced intervals. The distance separating the bolts can vary from about two feet to about four feet, depending upon the degree of support required. Basically, there are two kinds of roof bolts, depending on how the bolts are anchored in the roof: a mechanically anchored roof bolt and a resin-anchored roof bolt. The mechanically anchored roof bolt is point anchored in the roof by the physical interaction between the expandable point anchor and the rock surrounding the anchor. This is fine until there is movement in the rock formation surrounding the bolt. If such movement in the rock surrounding the bolt is extensive, the bolt may give and weaken its support. In tunnels where long term support is required, resin-anchored bolts are preferred. The resin-anchored bolt is anchored in the resin introduced into the bolt hole ahead of the bolt. The resin, once set, forms a hard, solid, chemically formed bond with the rock formation surrounding the bolt and along the entire length of the bolt. Such a resin anchor is considerably stronger and longer lasting than merely mechanically anchored roof bolts.
Automated and remote controlled machines have been developed to perform roof bolting operations in mines. These roof bolting machines are very expensive. They are expensive because they have to be both efficient and safe deep down in a mine. Due to these requirements, these machines have become rather complex. Anything improving their efficiency or reducing their complexity without adversely affecting their safety pays rich and continuing dividends in mining operations.
A roofbolting operation essentially entails drilling a long, narrow, vertical hole into the mine roof and inserting and anchoring a bolt in the hole. For the mechanically anchored roof bolt, these two steps only are required. For the resin-anchored roof bolt a third, intermediate step--resin insertion--is also required. Roof bolting machines feature two-position turrets for roofbolting with mechanically anchored roof bolts, and they feature three-position turrets for roofbolting with resin-anchored roof bolts. If resin bolting is desired with only a two-position turret available, the resin then must be inserted into the drilled hole by some means other than by the turret. Often, this involves manual insertion. Manual insertion exposes the operator to risk, however. Representative three-position roof bolter apparatus are disclosed in U.S. Pat. Nos. 4,215,953 and 4,229,124 to R. J. Perraud and G. R. Frey et al, respectively.
The three-position turret is, on the other hand, a rather complex and expensive piece of equipment. For, in addition to providing a separate means for inserting the resin into the drilled hole, it requires other features in support of this resin insertion operation. These additional features include a reaming bit and a reaming motor, together with associated components. These are needed to drill a cone-shaped collar around the entrance of the hole. Such a cone-shaped collar is necessary to guide the resin injection nozzle into position with respect to the hole. See U.S. Pat. No. 4,105,081 to R. J. Perraud. The presence of these additional features on the turret, in turn, requires further and more complicated accessories in the automated remote control system for the turret. All this has a mushrooming effect, especially as regards costs--both initial costs of manufacture and, perhaps more significantly, operational and maintenance costs of such roofbolting equipment.